Lithographic apparatus and device manufacturing method

ABSTRACT

The joint between the projection system element and its support comprises an inorganic layer or a direct bond and is thus liquid tight, which can prevent deformation by an immersion liquid. The joint can be made either warm or cold. Solders, glue, and glue protection can all be used in the formation of this joint. In an embodiment, the elements and its support are made of quartz.

FIELD

The present invention relates to a lithographic apparatus.

BACKGROUND

A lithographic apparatus is a machine that applies a desired patternonto a target portion of a substrate. Lithographic apparatus can beused, for example, in the manufacture of integrated circuits (ICs). Inthat circumstance, a patterning device, such as a mask, may be used togenerate a circuit pattern corresponding to an individual layer of theIC, and this pattern can be imaged onto a target portion (e.g.comprising part of, one or several dies) on a substrate (e.g. a siliconwafer) that has a layer of radiation-sensitive material (resist). Ingeneral, a single substrate will contain a network of adjacent targetportions that are successively exposed. Known lithographic apparatusinclude so-called steppers, in which each target portion is irradiatedby exposing an entire pattern onto the target portion in one go, andso-called scanners, in which each target portion is irradiated byscanning the pattern through the projection beam in a given direction(the “scanning”-direction) while synchronously scanning the substrateparallel or anti-parallel to this direction.

It has been proposed to immerse the substrate in the lithographicprojection apparatus in a liquid having a relatively high refractiveindex, e.g. water, so as to fill a space between the final element ofthe projection system and the substrate. The point of this is to enableimaging of smaller features since the exposure radiation will have ashorter wavelength in the liquid. (The effect of the liquid may also beregarded as increasing the effective NA of the system and alsoincreasing the depth of focus.)

However, submersing the substrate or substrate and substrate table in abath of liquid (see for example U.S. Pat. No. 4,509,852, herebyincorporated in its entirety by reference) may mean that there is alarge body of liquid that should be accelerated during a scanningexposure. This may require additional or more powerful motors andturbulence in the liquid may lead to undesirable and unpredictableeffects. Also, the optical properties, in particular the geometricaloptical properties of the elements of the projection system shouldremain constant.

One of the solutions proposed is for a liquid supply system to provideliquid on only a localized area of the substrate and in between thefinal element of the projection system and the substrate using a liquidsupply system (the substrate generally has a larger surface area thanthe final element of the projection system). One way which has beenproposed to arrange for this is disclosed in PCT patent application WO99/49504, hereby incorporated in its entirety by reference. Asillustrated in FIGS. 2 and 3, liquid is supplied by at least one inletIN onto the substrate, in an embodiment along the direction of movementof the substrate relative to the final element, and is removed by atleast one outlet OUT after having passed under the projection system.That is, as the substrate is scanned beneath the element in a −Xdirection, liquid is supplied at the +X side of the element and taken upat the −X side. FIG. 2 shows the arrangement schematically in whichliquid is supplied via inlet IN and is taken up on the other side of theelement by outlet OUT which is connected to a low pressure source. Inthe illustration of FIG. 2 the liquid is supplied along the direction ofmovement of the substrate relative to the final element, though thisdoes not need to be the case. Various orientations and numbers of in-and out-lets positioned around the final element are possible, oneexample is illustrated in FIG. 3 in which four sets of an inlet with anoutlet on either side are provided in a regular pattern around the finalelement.

SUMMARY

The presence of fluid around the bottom of a projection system maydeform elements of the projection system possibly leading to degradationof exposure. Further, the liquid may enter into the projection systemwhich can damage or deform delicate parts of the apparatus over time.

Accordingly, it would be advantageous to provide, for example, anapparatus in which distortion of the projection system due to thepresence of liquid is minimized.

According to an aspect, there is provided a lithographic apparatuscomprising:

-   -   a support structure configured to hold a patterning device, the        patterning device configured to pattern a projection beam with a        pattern in its cross-section;    -   a substrate table configured to hold a substrate; and    -   a projection system configured to project the patterned beam        onto a target portion of the substrate, wherein a joint between        an element of the projection system and its support comprises an        inorganic layer.

By making a joint liquid tight, i.e., no liquid can enter the projectionsystem, deformation of projection system element, such as a lens, may beminimized. In particular, deformation of the element should be limitedto the amount by which lens elements can compensate for the distortion.

In an embodiment, the joint can comprise a direct bond. Direct bondingis used as a broad term and encompasses fusion bonding, anodic bonding,compression bonding etc.

The inorganic layer can be a metal, ceramic or glass layer or glueprotection. The element of the projection system and its support can bemade of glass, bonding of which is relatively simple. In an embodiment,the element and its support are made of fused silica.

The apparatus may further comprise a liquid supply system configured toat least partly fill a space between the projection system and thesubstrate, with a liquid.

In an embodiment, the joints between all parts of the projection systemimmersed in liquid comprise an inorganic layer. Liquid can be preventedfrom entering the projection system or weakening any of the joints. Thejoint can be made liquid resistant by applying an inorganic layer to thejoint.

The joint can be made without any heating. For example, the joint can bemade liquid tight by applying a liquid resistant layer to the joint. Thejoint between the element of the projection system and its support (andother joints) can be made using glue (which need not be liquidresistant) or by the interaction of physically and chemically cleansurfaces. To clean the surfaces, a solvent could be applied or thesurfaces freshly cleaved. After a bonding, an inorganic layer could thenbe applied to the joint.

Alternatively, the joint can be heat treated. The joint may be heated toabout 900° C., in an embodiment for at least one hour. Again, the jointcan be made by the interaction of clean surfaces. For improved results,the glass may be doped with boron. An alternative warm joint is made bythe interaction of clean surfaces, sealed with a low temperature glasssolder and then heat treated to 600° C. A further type of warm joint isa metal solder. Indium solder has been found to work particularly well.

According to an aspect, there is provided a lithographic apparatuscomprising:

-   -   a support structure configured to hold a patterning device, the        patterning device configured to pattern a projection beam with a        pattern in its cross-section;    -   a substrate table configured to hold a substrate; and    -   a projection system configured to projecting the patterned beam        onto a target portion of the substrate, wherein a joint between        an of the projection system and its support comprises a direct        bond.

According to an aspect, there is provided an immersion projection systemmanufacturing method comprising joining an element of a projectionsystem, that in use in a lithographic apparatus comes into contact witha liquid, with its support using at least one of an inorganic layer ordirect bonding.

According to an aspect, there is provided a device manufacturing methodcomprising projecting a patterned beam of radiation onto a targetportion of the substrate through an element of a projection systemjoined to its support using at least one of an inorganic layer or directbonding.

Although specific reference may be made in this text to the use oflithographic apparatus in the manufacture of ICs, it should beunderstood that the lithographic apparatus described herein may haveother applications, such as the manufacture of integrated opticalsystems, guidance and detection patterns for magnetic domain memories,liquid-crystal displays (LCDs), thin-film magnetic heads, etc. Theskilled artisan will appreciate that, in the context of such alternativeapplications, any use of the terms “wafer” or “die” herein may beconsidered as synonymous with the more general terms “substrate” or“target portion”, respectively. The substrate referred to herein may beprocessed, before or after exposure, in for example a track (a tool thattypically applies a layer of resist to a substrate and develops theexposed resist) or a metrology or inspection tool. Where applicable, thedisclosure herein may be applied to such and other substrate processingtools. Further, the substrate may be processed more than once, forexample in order to create a multi-layer IC, so that the term substrateused herein may also refer to a substrate that already contains multipleprocessed layers.

The terms “radiation” and “beam” used herein encompass all types ofelectromagnetic radiation, including ultraviolet (UV) radiation (e.g.having a wavelength of 365, 248, 193, 157 or 126 nm).

The term “patterning device” used herein should be broadly interpretedas referring to any device that can be used to impart a projection beamwith a pattern in its cross-section such as to create a pattern in atarget portion of the substrate. It should be noted that the patternimparted to the projection beam may not exactly correspond to thedesired pattern in the target portion of the substrate. Generally, thepattern imparted to the projection beam will correspond to a particularfunctional layer in a device being created in the target portion, suchas an integrated circuit.

A patterning device may be transmissive or reflective. Examples of apatterning device include masks, programmable mirror arrays, andprogrammable LCD panels. Masks are well known in lithography, andinclude mask types such as binary, alternating phase-shift, andattenuated phase-shift, as well as various hybrid mask types. An exampleof a programmable mirror array employs a matrix arrangement of smallmirrors, each of which can be individually tilted so as to reflect anincoming radiation beam in different directions; in this manner, thereflected beam is patterned. In each example of a patterning device, thesupport structure may be a frame or table, for example, which may befixed or movable as required and which may ensure that the patterningdevice is at a desired position, for example with respect to theprojection system. Any use of the terms “reticle” or “mask” herein maybe considered synonymous with the more general term “patterning device”.

The term “projection system” used herein should be broadly interpretedas encompassing various types of projection system, including refractiveoptical systems, reflective optical systems, and catadioptric opticalsystems, as appropriate for example for the exposure radiation beingused, or for other factors such as the use of an immersion fluid or theuse of a vacuum. Any use of the term “lens” herein may be considered assynonymous with the more general term “projection system”.

The illumination system may also encompass various types of opticalcomponents, including refractive, reflective, and catadioptric opticalcomponents for directing, shaping, or controlling the projection beam ofradiation, and such components may also be referred to below,collectively or singularly, as a “lens”.

The lithographic apparatus may be of a type having two (dual stage) ormore substrate tables (and/or two or more mask tables). In such“multiple stage” machines the additional tables may be used in parallel,or preparatory steps may be carried out on one or more tables while oneor more other tables are being used for exposure.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying schematic drawings in whichcorresponding reference symbols indicate corresponding parts, and inwhich:

FIG. 1 depicts a lithographic apparatus according to an embodiment ofthe invention;

FIG. 2 depicts a liquid supply system according to an embodiment of theinvention;

FIG. 3 is an alternative view of the liquid supply system of FIG. 2according to an embodiment of the invention;

FIG. 4 is a view of a joint according to an embodiment of the invention;

FIG. 5 is a detailed view of the joint shown in FIG. 4;

FIG. 6 is a detailed view of an embodiment of the invention;

FIG. 7 is a detailed view of a joint according to an embodiment of theinvention;

FIG. 8 is a detailed view of a joint according to an embodiment of theinvention; and

FIG. 9 is a detailed view of a joint according to another embodiment ofthe invention.

DETAILED DESCRIPTION

FIG. 1 schematically depicts a lithographic apparatus according to aparticular embodiment of the invention. The apparatus comprises:

-   -   an illumination system (illuminator) IL for providing a        projection beam PB of radiation (e.g. UV radiation);    -   a first support structure (e.g. a mask table) MT for supporting        a patterning device (e.g. a mask) MA and connected to first        positioning means for accurately positioning the patterning        device with respect to item PL;    -   a substrate table (e.g. a wafer table) WT for holding a        substrate (e.g. a resist-coated wafer) W and connected to second        positioning means for accurately positioning the substrate with        respect to item PL; and    -   a projection system (e.g. a refractive projection lens) PL for        imaging a pattern imparted to the projection beam PB by        patterning device MA onto a target portion C (e.g. comprising        one or more dies) of the substrate W.

As here depicted, the apparatus is of a transmissive type (e.g.employing a transmissive mask). Alternatively, the apparatus may be of areflective type (e.g. employing a programmable mirror array of a type asreferred to above).

The illuminator IL receives a beam of radiation from a radiation source.The source and the lithographic apparatus may be separate entities, forexample when the source is an excimer laser. In such cases, the sourceis not considered to form part of the lithographic apparatus and theradiation beam is passed from the source to the illuminator IL with theaid of a beam delivery system comprising for example suitable directingmirrors and/or a beam expander. In other cases the source may beintegral part of the apparatus, for example when the source is a mercurylamp. The source and the illuminator IL, together with the beam deliverysystem if required, may be referred to as a radiation system.

The illuminator IL may comprise adjusting means for adjusting theangular intensity distribution of the beam. Generally, at least theouter and/or inner radial extent (commonly referred to as σ-outer andσ-inner, respectively) of the intensity distribution in a pupil plane ofthe illuminator can be adjusted. In addition, the illuminator ILgenerally comprises various other components, such as an integrator INand a condenser CO. The illuminator provides a conditioned beam ofradiation, referred to as the projection beam PB, having a desireduniformity and intensity distribution in its cross-section.

The projection beam PB is incident on the mask MA, which is held on themask table MT. Having traversed the mask MA, the projection beam PBpasses through the lens PL, which focuses the beam onto a target portionC of the substrate W. With the aid of the second positioning means andposition sensor IF (e.g. an interferometric device), the substrate tableWT can be moved accurately, e.g. so as to position different targetportions C in the path of the beam PB. Similarly, the first positioningmeans and another position sensor (which is not explicitly depicted inFIG. 1) can be used to accurately position the mask MA with respect tothe path of the beam PB, e.g. after mechanical retrieval from a masklibrary, or during a scan. In general, movement of the object tables MTand WT will be realized with the aid of a long-stroke module (coarsepositioning) and a short-stroke module (fine positioning), which formpart of the positioning means. However, in the case of a stepper (asopposed to a scanner) the mask table MT may be connected to a shortstroke actuator only, or may be fixed. Mask MA and substrate W may bealigned using mask alignment marks M1, M2 and substrate alignment marksP1, P2.

The depicted apparatus can be used in the following modes:

-   -   1. In step mode, the mask table MT and the substrate table WT        are kept essentially stationary, while an entire pattern        imparted to the projection beam is projected onto a target        portion C in one go (i.e. a single static exposure). The        substrate table WT is then shifted in the X and/or Y direction        so that a different target portion C can be exposed. In step        mode, the maximum size of the exposure field limits the size of        the target portion C imaged in a single static exposure.    -   2. In scan mode, the mask table MT and the substrate table WT        are scanned synchronously while a pattern imparted to the        projection beam is projected onto a target portion C (i.e. a        single dynamic exposure). The velocity and direction of the        substrate table WT relative to the mask table MT is determined        by the (de-)magnification and image reversal characteristics of        the projection system PL. In scan mode, the maximum size of the        exposure field limits the width (in the non-scanning direction)        of the target portion in a single dynamic exposure, whereas the        length of the scanning motion determines the height (in the        scanning direction) of the target portion.    -   3. In another mode, the mask table MT is kept essentially        stationary holding a programmable patterning device, and the        substrate table WT is moved or scanned while a pattern imparted        to the projection beam is projected onto a target portion C. In        this mode, generally a pulsed radiation source is employed and        the programmable patterning device is updated as required after        each movement of the substrate table WT or in between successive        radiation pulses during a scan. This mode of operation can be        readily applied to maskless lithography that utilizes a        programmable patterning device, such as a programmable mirror        array of a type as referred to above.

Combinations and/or variations on the above described modes of use orentirely different modes of use may also be employed.

In addition to the liquid supply solutions described above, anothersolution which has been proposed is to provide the liquid supply systemwith a seal member which extends along at least a part of a boundary ofthe space between the final element of the projection system and thesubstrate table. The seal member is substantially stationary relative tothe projection system in the XY plane though there may be some relativemovement in the Z direction (in the direction of the optical axis). Aseal is formed between the seal member and the surface of the substrate.In an embodiment, the seal is a contactless seal such as a gas seal.Such a system is disclosed in European Patent Application No. 03252955.4and U.S. patent application Ser. No. 10/705,783, hereby incorporated inits entirety by reference.

In FIGS. 4 and 5, the final element, e.g. a lens 21, of the projectionsystem is shown together with its support 22. In this example both thelens 21 and the support 22 are made of fused silica but could be made ofanother glass or any other transparent material. Indeed the lens 21 andthe support 22 need not be made of the same material. Ideally, however,their expansion coefficients should be similar. For example, a higherquality material may be used for the lens 21 and a lower qualitymaterial for the support 22. A glue 23 joins the lens 21 and the support22 together. Once the glue has set a liquid tight layer of glueprotection 24 is applied to the joint. The glue protection 24 is appliedto the entire joint. No parts are left uncovered.

In FIG. 6, the surfaces of the lens 21 and the support 22 to be joinedare smoother and physically and chemically cleaned. The surfaces are soclean and smooth that the molecules in the lens 21 and support 22 beginto interact chemically by so-called “direct bonding”, forming a bondbetween the lens and support. To assist and expedite this process thelens 21 and support 22 can be pressed together for a time. This type ofbonding is particularly suitable for this situation as it producesminimal distortion of the original materials, maintains the qualities ofthe original materials and is strong. Additionally, glue sealing 25 canbe applied to the joint followed by glue protection 24 covering theentire of the joint area.

The joint can also be made warm. In FIG. 7, a bond between the lens andsupport has been made by joining two physically and chemically cleansurfaces, as in FIG. 6 and then heat treated at 900° C. for at least onehour, in an embodiment at least six hours. The bonds between the lens 21and support 22 then become covalent bonds which are particularly strongand watertight, as described in Materials Science Engineeringincorporated herein in its entirety. The (glass) lens 21 and/or support22 can be covered by a thin layer of boron prior to the bonding. Theboron diffuses into the lens 21 and/or support 22 where it aids bondingof the molecules concerned and reduces local stresses and strains.Annealing can therefore take place at a lower temperature than if boronwere not present and covalent bonds will still be formed. This processis described in more detail in Philips Journal of Research 49 (1995)pages 152-153, incorporated herein in it entirety by reference.

In FIG. 8, the joint has been made by bonding two physically andchemically clean surfaces (as in FIGS. 6 and 7) and then sealed with alow temperature solder 27. The solder should have the same compositionas the lens 21 and the support 22. The joint is then heat treated atabout 600° C.

In FIG. 9 an indium solder 28 is used between the lens 21 and thesupport 22. Although indium is used in an embodiment, other metals canalso be used.

Although the joint between the lens 21 and its support 22 has beendescribed here it will be obvious to the skilled person that the sametechnology can be applied to any other joint in the projection system,and indeed in the lithographic apparatus. In particular, all jointswhich may come into contact with the immersion liquid should be madeliquid tight by one of the methods described above.

While specific embodiments of the invention have been described above,it will be appreciated that the invention may be practiced otherwisethan as described. The description is not intended to limit theinvention.

1. A lithographic apparatus comprising: a support structure configuredto hold a patterning device, the patterning device configured to patterna projection beam with a pattern in its cross-section; a substrate tableconfigured to hold a substrate; and a projection system configured toproject the patterned beam onto a target portion of the substrate,wherein a joint between an element of the projection system and itssupport comprises an inorganic layer.
 2. A lithographic apparatusaccording to claim 1, further comprises a liquid supply systemconfigured to at least partially fill a space between the projectionsystem and the substrate, with a liquid.
 3. A lithographic apparatusaccording to claim 2, wherein the element comes into contact with theliquid.
 4. A lithographic apparatus according to claim 1, wherein theinorganic layer comprises at least one of a metal, ceramic and glasslayer.
 5. A lithographic apparatus according to claim 4, wherein theinorganic layer is glue protection.
 6. A lithographic apparatusaccording to claim 1, wherein said joint comprises a direct bond.
 7. Alithographic apparatus according to claim 1, wherein the joint was madewithout heating.
 8. A lithographic apparatus according to claim 1,wherein the joint was heat treated.
 9. A lithographic apparatusaccording to claim 8, wherein the joint has been heat treated to 900° C.10. A lithographic apparatus according to claim 8, wherein the joint ismade by the interaction of clean surfaces.
 11. A lithographic apparatusaccording to claim 8, wherein the joint is made by the interaction ofclean surfaces, sealed with a low temperature glass solder and heattreated to 600° C.
 12. A lithographic apparatus according to claim 8,wherein the element of the projection system and its support are dopedwith boron.
 13. A lithographic apparatus according to claim 12, whereinthe joint is made by the interaction of clean surfaces, sealed with alow temperature glass solder and heat treated to 600° C.
 14. Alithographic apparatus according to claim 1, wherein the inorganic layercomprises a metal solder.
 15. A lithographic apparatus according toclaim 14, wherein the metal solder is indium.
 16. A lithographicapparatus according to claim 1, wherein the element and its support aremade of glass.
 17. A lithographic apparatus according to claim 16,wherein the element and its support are made of fused silica.
 18. Alithographic apparatus according to claim 1, wherein the joints betweenall parts of the projection system immersed in a liquid comprise aninorganic layer.
 19. A lithographic apparatus according to claim 1,wherein the element is a lens.
 20. A lithographic apparatus comprising:a support structure configured to hold a patterning device, thepatterning device configured to pattern a projection beam with a patternin its cross-section; a substrate table configured to hold a substrate;and a projection system configured to project the patterned beam onto atarget portion of the substrate, wherein a joint between an of theprojection system and its support comprises a direct bond.
 21. Alithographic apparatus according to claim 20, further comprises a liquidsupply system configured to at least partially fill a space between theprojection system and the substrate, with a liquid.
 22. A lithographicapparatus according to claim 21, wherein the element comes into contactwith the liquid.
 23. A lithographic apparatus according to claim 20,wherein the joint comprises at least one of a metal, ceramic and glasslayer.
 24. A lithographic apparatus according to claim 23, wherein thejoint comprises a layer of glue protection.
 25. A lithographic apparatusaccording to claim 20, wherein the joint was made without heating.
 26. Alithographic apparatus according to claim 20, wherein the joint was heattreated.
 27. A lithographic apparatus according to claim 26, wherein thejoint has been heat treated to 900° C.
 28. A lithographic apparatusaccording to claim 26, wherein the joint is made by the interaction ofclean surfaces.
 29. A lithographic apparatus according to claim 26,wherein the joint is made by the interaction of clean surfaces, sealedwith a low temperature glass solder and heat treated to 600° C.
 30. Alithographic apparatus according to claim 26, wherein the element of theprojection system and its support are doped with boron.
 31. Alithographic apparatus according to claim 30, wherein the joint is madeby the interaction of clean surfaces, sealed with a low temperatureglass solder and heat treated to 600° C.
 32. A lithographic apparatusaccording to claim 20, wherein the joint comprises a layer of metalsolder.
 33. A lithographic apparatus according to claim 32, wherein themetal solder comprises indium.
 34. A lithographic apparatus according toclaim 20, wherein the element and its support are made of glass.
 35. Alithographic apparatus according to claim 34, wherein the element andits support are made of fused silica.
 36. A lithographic apparatusaccording to claim 20, wherein the joints between all parts of theprojection system immersed in a liquid comprise an inorganic layer. 37.A lithographic apparatus according to claim 20, wherein the element is alens.
 38. A lithographic apparatus comprising: a support structureconfigured to hold a patterning device, the patterning device configuredto pattern a projection beam with a pattern in its cross-section; asubstrate table configured to hold a substrate; and a projection systemconfigured to project the patterned beam onto a target portion of thesubstrate, the projection system having a lens, a lens support and aninorganic material providing a fluid tight seal between the lens and thelens support.
 39. A lithographic apparatus according to claim 38,wherein the inorganic layer comprises at least one of a metal, ceramicand glass layer.
 40. A lithographic apparatus according to claim 38,further comprising a direct bond between the lens and the lens support.41. A lithographic apparatus according to claim 38, wherein the lens andthe lens support are made of glass.
 42. A lithographic apparatuscomprising: a support structure configured to hold a patterning device,the patterning device configured to pattern a projection beam with apattern in its cross-section; a substrate table configured to hold asubstrate; and wherein a joint between an of the projection system andits support comprises a direct bond. a projection system configured toproject the patterned beam onto a target portion of the substrate, theprojection system having a lens, a lens support and a direct bondproviding a fluid tight seal between the lens and the lens support. 43.A lithographic apparatus according to claim 42, further comprising atleast one of a metal, ceramic and glass layer at a joint between thelens and the lens support.
 44. A lithographic apparatus according toclaim 42, wherein a joint between the lens and the lens support was heattreated.
 45. A lithographic apparatus according to claim 42, wherein thelens and the lens support are made of glass.
 46. An immersion projectionsystem manufacturing method comprising joining an element of aprojection system, that in use in a lithographic apparatus comes intocontact with a liquid, with its support using at least one of aninorganic layer or direct bonding.
 47. The method according to claim 46,wherein said inorganic layer comprises at least one of a metal, ceramicand glass layer.
 48. The method according to claim 46, comprising heattreating the element and its support.
 49. The method according to claim48, wherein the joining comprises creating a joint by the interaction ofa clean surface of the element and a clean surface of the support. 50.The method according to claim 46, wherein the inorganic layer comprisesmetal solder.
 51. The method according to claim 46, wherein the elementand its support are made of glass.
 52. The method according to claim 51,wherein the element and its support are made of fused silica.
 53. Themethod according to claim 46, comprising joining all elements of theprojection system immersed in a liquid with their respective supportsusing an inorganic layer.